Improvement in hardening cast-iron



NITED STATES THOMAS ALLIN, OF NEW YORK, N. Y.

Specification forming part of Letters Patent No. 42,453, dated April 26, 1864.

To all whom it may concern:

Be it known that I, THOMAS ALLIN, of the city, county, and State of New York, have inrented a certain new and useful Process for Hardening Cast-Iron; and 1 doherebydeclare that the following is a full, clear, and exact description thereof.

The object of my said process is to harden cast-iron that it may be substituted for hardened steel for many purposes in the arts.

Although the well-known process of chilling cast-iron by running it in the molten state into cold iron molds renders it very hard, and for many purposes, when so hardened, it is very useful, still the process is not applicable to the production of articles which require to be made true and with smooth surfaces, for the reason that it is too hard to be worked after being so chilled; but by my said process I can render cast-iron as hard as hardened steel after it has been cast and suffered to set in the mold or to cool in the ordinary way and worked by turning, filing, or other means to the required form and surface.

I take the cast-iron, after it has been cast in the usual way or in any other suitable way, but not chilled, and when desired, after it has been worked by turning, filing, or cutting, and heat it slowly in any suitable furnace or oven until it reaches about a blood-red heat, and I then plunge it inacold acid bath composed in the proportion of one pound of sulphuric acid, one ounce ofnitric acid, and one gallon of water, and move the iron in it until it becomes cold. When taken out it will he found to have acquired a degree of hardness equal to heated to a blood-red heat; but I do not wish to be understood as limiting my claim of invention to such degree of heat, as a slight y'ariation will not materially affect the result;

and although I have above stated that I take the oastiron after it has been taken out of the mold, cooled, and then heat it to a cherry-red heat to plunge it in the acid bath, I have so described my process because for most purposes it is important to work the cast-iron by turning,'cutting, or filing before it is hardened; but when this is not required the castiron can be taken directly from the mold before it cools down below a cherry-red heat, and in that condition plunged in theacid bath.

What I claim as my invention, and desire to secure by Letters Patent, is-- The process, substantially 'as above described, of hardening cast-iron by plunging it in a bath of acid and water when it is atabout a blood-red heat, vsubstantially as set forth.

THOMAS ALLIN.

Witnesses:

DE LACY, X M. H. BIsHOP. 

